Dosage-dispensing devices of this kind find application in particular in dispensing small quantities, for example of toxic substances, with high precision into small target containers. Frequently, such recipient containers are placed on a balance in order to weigh the substance delivered out of the dosage-dispensing device, so that the substance can subsequently be further processed according to given specifications.
The substance to be dispensed is contained for example in a source container which is equipped with a dispensing head. It is desirable to deliver the substance to the outside through a small outlet opening in the dosage-dispensing device, so that the substance can be filled in a targeted stream into a container with an opening of narrow cross-section.
Dosage-dispensing devices for dry and/or powdery substances of a pourable consistency, for example color pigments belong to the known state of the art and are in current use. For example in U.S. Pat. No. 5,145,009 A, a dosage-dispensing device is described which consists of a source container with a closable outlet at its underside. As a closure element, the device has a cone-shaped valve body which is narrower towards the top, is vertically movable in the downward direction to open an outlet orifice, is rotatable when in the open position, and is equipped with means for advancing the substance towards the outlet opening. Furthermore, a drive shaft passes through the source container, extending beyond the topside of the latter, where it is coupled to a drive mechanism. The source container has at its underside a connecting flange that attaches to the dosage-dispensing device. Several pressure cylinders act on the cover of the source container, whose stroke travel allows the outlet opening and thus the rate of delivery from the source container to be controlled. The valve body in dosage-dispensing devices of this kind needs to be seated in the source container with as little free play as possible in order to allow an accurate control of the substance doses being dispensed. Furthermore, dispensing of doses in the microgram range requires very rigid connections between the drive mechanism and the source container seated in place, because in the final phase of the dosage-dispensing process the remaining substance quantity is released by minute changes in the angle of rotation and the vertical stroke position of the valve body.
In view of the requirements that are placed on the attachment of the source container in the dosage-dispensing device, the arrangement of the foregoing description has the disadvantage that the source container and the mechanical interface connections of the dosage-dispensing device to the source container have to be matched to each other very precisely in order to allow the drive shaft to be coupled to the drive mechanism when the source container is set into the dosage-dispensing device. The tight tolerances on fit and position associated with this requirement make the parts very expensive to produce. Furthermore, depending on the design of the connecting flange, setting the source container into place is a time-consuming operation due to the required alignment operations. This dosage-dispensing device is therefore strongly dependent on the infrastructure at the location where it is installed.